Converting a straight grip Marlin to a pistol grip is generally not a matter of "gunsmithing." It simply requires the replacement (substitution) of 3 or 4 pistol grip parts for the straight grip parts. If you have the parts, replacing them is pretty easy.
The problem is: You have to see if Marlin made the 1894 in pistol grip configeration in stainless. If so, then you just need to figure out what Marlin parts you need and buy them. Of course, one of the parts you will need will be a totally new butt-stock, which is not cheap and there is no guarantee that the shade of the wood will match the forestock that you currently have.
If Marlin did not make the 1894 in pistol grip stainless, then I think you are out of luck. Maybe just maybe there is some custom gunsmith out there that does this work, but you are probably going to spend more than the price of the rifle to get it done.
I love a straight grip. Much quicker to shoulder and, for me, handier to carry.
You may want to post this question on the Cowboy shooting board, because those folks spend their lives living and breathing this type of stuff. And, they will probably know a custom gunsmith.
Best Regards,
Mannyrock
